In 2002 the US Department of Energy began hosting the bi-annual Solar Decathlon, an event that challenges college students to design and build a solar-powered house that’s affordable, energy efficient, and appealing. Among the twenty teams competing in this year’s event is Team Capitol DC: a consortium that includes The Catholic University of America, George Washington University, and American University. Team Capitol DC designed and built the Harvest Home, so named because it harvests natural resources, including sunlight, airflow, water, and a food-producing garden. In addition to being a great learning activity for students, an excellent demonstration of sustainable building techniques, and a fine example of renewable energy, the project will also support wounded American veterans.Team Capitol DC will donate the completed house to Wounded Warrior Homes in San Diego, where it will be used as a transitional home for American veterans wounded in the Iraq and Afghanistan wars. Four good causes in one project!
The house is designed for the southern California climate, making solar a pretty obvious choice for power. It includes a 7.84 kW photovoltaic array that covers most of the roof. Microinverters, which decrease the negative effects of a partially shaded array, convert the DC to AC and tie the house to the grid. With an annual average of 5.62 Peak Sun Hours, the array is expected to generate about 13,000 kWh annually. That’s slightly higher than the average household electrical consumption, according US Department of Energy statistics. And since the house was designed with energy efficiency in mind, it’s actually twice as much electricity as the home is expected to use. This will allow the homeowner to sell electricity back to the grid. From a net-metering standpoint, I think that’s an over-designed system. Net-metering gives the consumer credits but doesn’t allow homeowners to make a profit by selling excess energy. At best this owner will pay no electric bill. Maybe he can set up an electric vehicle charging station and collect a few dollars by allowing neighbors to charge their vehicles!
Water is heated with a flat-plate collector that feeds an 80-gallon holding tank. The tank includes an auxiliary heating element for cloudy days. I’m guessing the auxiliary unit won’t have to fire up very often. A central air conditioner/heat pump with a SEER of 17.5 provide both cooling and heating for the home. Heat pumps are very good sources of heat, with an “apparent efficiency” near 400%, meaning they produce four times as much energy as the electricity they consume. No, that’s not a violation of the First Law of Thermodynamics - they’re extracting “free energy” from the ambient heat outside. (That’s why I called it “apparent efficiency.”) In warm climates that’s an obvious choice, but even in the cold northern US where I live, an efficient heat pump is a great source of heat. In any event, an energy-efficient house in southern California isn’t likely to use the heat pump very often.
Speaking of energy efficient design, the home includes double pane low-E windows, an interactive shade screen over south-facing windows, structurally insulated panels (SIPs), a tight thermal envelope, and a white roof. Its passive solar design includes a lot of windows and plenty of natural ventilation. Rainwater collection and a greywater system provide irrigation for the landscaping. The Harvest Home is constructed from reclaimed and recycled non-toxic materials, promoting a healthy indoor air quality. The house is in the process of obtaining the LEED for Homes certification.
Since the home will be donated to a wounded veteran, it’s also designed to be a healing environment. The Harvest Home includes a smart home management system (control unit pictured above) that allows its occupant to monitor and control the appliances with little effort. It is ADA compliant and includes landscaping to promote general peace and well being.
Here’s a short video from Team Capitol DC describing the Harvest Home:
The Harvest Home cost approximately $290,000 to build, including labor and PV panels. While you may think that a house like this would only be practical in warmer climates, passive and active solar techniques are actually quite efficient even in the northern regions. With a few small adjustments, the Harvest Home would work almost anywhere in the world.
If you’d like to donate to the Harvest Home, click here. I think it’s a worthy cause on several levels!
Images and video: Team Capitol DC